ON THE HYDRATES M(HSEO3)2-CENTER-DOT-4H2O (M=MG, CO, NI, ZN) - CRYSTAL-STRUCTURES, IR, RAMAN, AND THERMOANALYTICAL INVESTIGATIONS

From aqueous solutions of M(HSeO3)2 single crystals of Mg(HSeO3)2 . 4H 2O and of the hitherto unknown compounds Co(HSeO3)2 . 4H2O, Ni(HSeO3)2 . 4H2O and Zn(HSeO3)2 . 4H2O could be obtained. The crystal structure s, X-ray powder, IR, Raman and thermoanalytical (DTA, TG, Raman heatin g) data are presented and discussed. The crystal data of the isotypic compounds are: monoclinic, space group C2/c, Z = 4, Mg: a = 1 464.6(2) , b = 755.3(1), c = 1099.9(1) pm, beta = 126.59(1)-degrees, V = 0.9769 (1) nm3, Co: a = 1 462.5(2), b = 756.5(2), c = 1 102.2(2) pm, beta = 1 26.5391)-degree, V = 0.9798(2) nm3, Ni: a = 1 452.2(2), b = 751.0(1), c = 1 091.5(1) pm, beta = 126.28(1)-degree, V = 0.9595(1) nm3, Zn: a = 1468.3(2), b = 755.8(1), c = 1103.1(1) pm, beta = 126.79(1)degree, V = 0.9804(2) nm3. The crystal structures consist of hexagonal packed [M (HSeO3)2 . 2H2O]n chains of [MO4(H2O)2] octahedra linked by Se atoms. They contain trigonal pyramidal SeO2OH-ions with ''free'' hydroxyl gro ups and also ''free'' molecules of water of crystallization. The hydro xyl groups build strong H-bonds (O-H ...O distances: 265-268 pm). The IR spectra show AB doublett bands in the OH stretching mode region of the hydroxyl groups. The water molecules of crystallization are linked to planar (H2O)4 tetramers by H-bonds with unusually short O-H ... O bond distances of 271-273 pm. DTA and TG measurements indicate that th ermal decomposition results in the direct formation of the respective diselenite MSe2O5. Raman heating measurements show under quasi static conditions the intermediate formation of the anhydrous hydrogen seleni tes.